Zero Waste Europe has given evidence that pyrolysis technology is extremely limited in producing recycled plastics. In a new report, ‘Leaky loop “recycling”: a technical correction on the quality of pyrolysis oil made from plastic waste’, the association argues that for pyrolysis oil to be used in the production of recycled plastic, it should either apply multiple energy-intensive purification steps or highly dilute the oil with virgin petroleum naphtha. Since neither option is in line with the ambitions of the EU Green Deal, pyrolysis is not the ‘miraculous’ key to a circular plastic economy, Zero Waste Europe concluded.
The report focusses on steam or naphtha cracking processing of pyrolysis oil. It puts forward evidence from a recent review of ‘many empirical research studies’ to disprove widely held industry claims that (1) pyrolysis oil is a drop-in replacement of virgin naphtha, (2) pyrolysis produces ‘virgin-like’ recycled plastics, (3) pyrolysis can recycle ‘difficult-to-recycle’ plastics.
Zero Waste Europe argues that (1) “raw pyrolysis oil made from plastic waste cannot be used as a 'drop-in' feedstock for naphtha steam crackers due to the carry-over of multiple contaminants and also the synthesis of unsuitable hydrocarbon chemistry.” Moreover, (2) raw pyrolysis oil made from plastic is unsuitable for making into plastic for contact-sensitive applications, i.e. for toys and/or for oral and skin applications, as such materials would breach the REACH regulatory limits. The same pyrolysis oils would also likely be classified as having acute and chronic aquatic toxicity according to the CLP Regulation, while some would also be classified as carcinogenic.” And finally (3), “those who make claims about pyrolysis being able to handle highly mixed, difficult-to-recycle plastic wastes are doing their industry no favours because the veracity of such common claims is challenged by lack of supporting evidence, is disputed by independent authors, conflicts with well-established science, and perhaps most tellingly - is refuted by pyrolysis operators.”
The association then argued that to bring pyrolysis oil ‘on specification’ to be used in steam crackers, it must either be purified in multiple, energy-intensive steps, or be blended with virgin naphtha.
“While extra energy will be needed for upgrading the oil, blending will mean lock-in to a future of more fossil carbon consumption. The question is therefore, how much blending would be required to bring plastic pyrolysis oil ‘on specification’ or in other words, how much plastic can actually make the round trip from plastic to plastic via pyrolysis. This question has so far only been assessable by LCAs which are widely criticised as untrustworthy for their incorrect energy costs and simplistic assumption that all the raw pyrolysis oil is useable,” the association claimed.
In its own calculations, it estimated the plastic mass losses during the pyrolysis to steam cracking process and final blending ratios of pyrolysis oil to petroleum naphtha using data from independent studies. It assumed a minimum pyrolysis oil yield of 5% and a maximum of 89%, and dilution factors ranging from 0.023 (ratio of over 40:1) to 0.045.
“Multiplying the range of oil yields taken from empirical studies of (largely polyolefins) plastic waste pyrolysis by the amount of petroleum naphtha recommended as necessary diluents to bring pyrolysis oil on specification for steam cracking (in terms of olefin limit value of 2 %), data show that over 99.9 % of the steam cracker input will need to be petroleum naphtha. In other words, even in the best-case scenario, only 2% of the plastic waste fed into pyrolysis will actually make the round trip into the steam cracker, and at worst less than 1% of plastic will be recycled,” Zero Waste Europe concluded.
This chilling result is important, the associated claimed, to push back on industry’s calls for free allocation of recycled content using the mass balance approach.
“Industry is pushing for permissive flexible allocation which would permit a product put on the market to be claimed as 100% recycled, even if for example only 1% of its composition is a recyclate and the other 99% comes from virgin petroleum. As this study has shown such accounting methods, in one simple measure bypass all the inherent difficulties of pyrolysis, while at the same time enabling it to be falsely represented as ‘green'. The analyses and results presented here support calls for proportional allocation which offers the least freedom and greatest environmental benefit, also reflecting the inherent and substantial imperfections of pyrolysis and on what this technology will actually be able to deliver,” the association concluded.